1. Field of the Invention
The present invention relates to electronic devices having a low number of leads with predefined functions, and especially portable electronic devices of the "SMARTCARD" type. The present invention more specifically relates to the testing of such electronic devices.
2. Discussion of the Related Art
FIG. 1 schematically shows the internal structure of an electronic device 10 of the "SMARTCARD" type. The device includes a microcontroller 12, or core, coupled to a peripheral 14 by a conventional bus including data lines D, address lines A, and control lines C. Further, microcontroller 12 receives interruptions INT from peripheral 14.
The device only includes eight leads having very precise functions. Two leads, Vdd and Vss, are used to supply the device. An input/output lead I/O forms the only input path to microcontroller 12. Peripheral 14 is connected to a data input lead Din and to a data output lead Dout. The microcontroller is clocked via a clock lead CLK while peripheral 14 is clocked independently via a clock lead DCLK. A general reset lead RST is used to reset all elements of device 10.
The devices of the type of FIG. 1 are often used to decrypt data. In this case, the encrypted data arrive on lead Din, undergo processing in peripheral 14 determined by microcontroller 12, and come out decrypted through lead Dout. The data are processed asynchronously with respect to the operation of the microcontroller, which explains the use of two clocks CLK and DCLK. The key used for the decryption, which thus determines the processings to be performed by peripheral 14, is stored inaccessibly in microcontroller 12. Thus, for security reasons, the possibilities of action upon microcontroller 12 via lead I/O are limited.
Lead I/O especially enables setting microcontroller 12 in a test mode to perform an exhaustive test of the microcontroller. Lead I/O then is by default in the input mode.
The several actions authorized from the outside on microcontroller 12 are obtained by exchanging information through lead I/O according to a predefined protocol.
A disadvantage of such a device is that its possibilities, especially for testing, are particularly limited due to the low number of leads all having assigned functions and due to the fact that the possibilities of access to the device via lead I/O are limited for security reasons.
Further, microcontroller 12 being programmed to interpret the protocol, perform the required actions, and return the results via lead I/O, the actions must remain simple in order not to increase the memory capacity of the microcontroller and thus the size of the device. The programming no longer allows the protocol to vary.
Finally, this device is poorly adapted to the testing of complex peripherals, since the tests performed, as they are extremely varied, are difficult to codify with a protocol. The information to be sent back to the microcontroller through data lines D or interrupt lines INT can only be established after the execution of complex sequences which are difficult to integrate to the protocol.